The present invention relates generally to a method for processing of hot, liquid slags and more particularly to a method for processing of hot, liquid slags that occur in smelting furnaces (e.g., blast furnaces or cupola furnaces)
In such a method, the slags to be processed are fed with a grainy material into a fluidized bed for granulation (for use as a raw material). The temperature of the fluidized bed is below the solidification temperature of the slag, and thus it is cooled down to below its solidification temperature while simultaneously forming granules.
Industrially occurring slags are known to be mixtures of silicates, perhaps also sulfides, chlorides, fluorides and other metal compounds generated in a smelt flow, which contain gangue from metallurgical smelting processes as well as other undesirable constituents from the smelting process.
For example, in ferrous and non-ferrous metallurgy, or in blast furnace slags, the ores (e.g., SiO.sub.2, CaO, MgO, Al.sub.2 O.sub.3), the coke ash, and the smelting additives, result from the gangue. The slags are primarily silicates and have been added to pick up harmful components and impurities (primarily sulfur).
Additionally, during the purifying process so-called Thomas slags are generated. Also, in the Siemens-Martin process basic or acidic slags are encountered, as are found in the operation of electric arc furnaces. Other examples of processes that generate a continuous, considerable volume of slags are found in reduction and refining processes in non-ferrous metal extraction and in cast iron production. In a cupola furnace, slags are formed from the ash of the coke, the sand and soot adhering to batch material, and from the scale and additives.
Although slags in metallurgy and foundry engineering are in a strict sense a "waste product," it is by no means true that this "byproduct" is of no value. Rather, slags represent a quite valuable raw material for other uses (e.g., for cement or glass production). To be able to recover slags in a suitable manner, they need to be processed after they emerge in a hot, liquid condition. For example, the cement industry needs glass-like, solidified, amorphous slags, while the glass industry desires a crystalline solid. Both of these examples, as well as other application examples (e.g., in road building), require that the slags be processed after their generation in order to alter their structure.
In a known method the hot slags flowing out of a smelting unit are quenched in a water stream traveling at relatively high speed and are thus broken into granules. Although this method provides good raw material, a limitation of this method is that mechanical and/or environmental problems are encountered that cannot be readily solved. For example, water pollution is particularly problematic, and the highly corrosive vapors generated on a large scale during this wet quenching-granulation process are difficult to satisfactorily handle.
One disadvantage of the wet granulation process is that wet-processed slags have a limited storage life, since wet-stored slags tend to solidify after a certain time due to their hydraulic properties. Consequently, any further processing of wet-processed slags will require an energy-intensive drying process beforehand. Furthermore, the tangible heat of the slag cannot be recovered from a wet granulation process.
In spite of the considerable disadvantages enumerated above, the wet granulation process is still being practiced on a significant scale. The considerable disadvantages are either accepted or taken into account in order to manage at least to some degree the considerable slag volumes produced and to obtain a raw, granulated material that is recovered for further use.
The article by H. W. Gudenau, K. H. Lindner, H. Maas and K. H. Peters, "Recovery of Waste Heat from Slags", in the German language journal "Stahl und Eisen", 106 (1986) no. 23, pp. 1281-1286, discloses a method belonging to the type described above, and an apparatus to implement this method ("Merotec-Slag Granulating System;" see page 1282, right column, f. and FIG. 3). The fundamental idea of this granulation method is to cool the liquid slags quickly, not with water as before, but rather by injecting a fine-grained, cold, recycled material into a thin, liquid slag film.
For each ton of liquid slag (at a temperature of about 1300.degree. C.) about one ton of material having a grain size less than 3 mm is injected, and a granulate at a temperature of about 600.degree.-700.degree. C. is produced which is sifted after cooling. When processing a blast furnace slag, 90 to 95% of the material is obtained in a granular range smaller than 5 mm.
Although this known method is clearly superior to wet granulation processes because the disadvantages enumerated above are largely avoided, it nevertheless still has considerable disadvantages. For example, the accelerator wheel which accelerates the fine-grained, cold slags into the hot, liquid slags, is subjected to severe wear. Additionally, wear also occurs on the agitators located in the fluidized bed.
In addition, it turns out that up to 86% of the slag end-product contains granules that are smaller than 3 mm, so that a granulate is obtained (with a glass content of about 80%) that cannot be used either in the cement industry nor in the production of insulating concrete and thermal-insulating building blocks since its density of 1.3 g/cm.sup.3 yields too large a bulk weight. This fine granulate is unsuitable for antifreeze-layers and support layers in road construction.
In view of the prior art, there is a need for providing a method and apparatus for processing hot, liquid slag in which there is a significant reduction in the wear of the system components; in which the process can be performed on a continuous basis; and in which the slag granulate obtained has significantly better granulation with a considerable reduction in fines and very fine fractions so that the slag end-product can be used as a raw material for any one of many potential purposes. Moreover, the greatest possible heat recovery should be achieved, particularly through the generation of steam and/or hot water.